Manual indexing is the operator task of visually locking onto text on an image and transcribing it into an electronic form by keying. Such work may be performed, for example, by human operators assigned to perform manual validation of results of an automated document capture process. Documents are scanned and data values are extracted automatically. For example, extraction may be done by OCR (optical character recognition), but OCR is rarely 100% accurate. In cases of doubt, or OCR is incorrect, or when a validation rule indicates an error, a human operator may be required to compare the extracted data to the image of the scanned document to determine if the correct value was extracted and if not to enter a correction.
The time it takes to lock onto text is generally described by Fitts' Law, a model that relates human movement as a function of the distance to and size of target. In short, the shorter the distance and larger the target, the less the targeting time.
A source of eye strain due to prolonged manually indexing work may come from one or both of the following two areas: 1) large repetitive movements, and 2) locking onto a narrow area (tunnel vision). Indexing in a commercial setting may require the operator to enter data at a rate of a field every 1.5 seconds or better, continuously for 8 hours per day (with a break every hour), for example.